Africa welcomes me back. I am as you left me. I Am. Unapologetic and uncompromising, the vast blank of the Sahara is a gigantic “why?” after the neat and productive terraforming of Europe. It scrolls past at 800 kilometres per hour, for hour upon hour, horizonless, fading into the distant haze in every direction.

Rocky plateaus form dark scabs and scrapes across the smooth faded-orange desert floor, fringed by deep-shadowed canyons that exist unto themselves, no explanation required. Ancient rivers cut dry, serpentine patterns in the crust, the ghosts of a climate past.

Featureless, country-sized sand plains make it seem like I’m suspended motionless in the sky. This Africa is utterly untamed, effortlessly aloof, ancient, silent. It is a million sunrises, a million sunsets, with sand and rock the only witness, never visited by the hand or foot of man.

I watch fantastical shapes far below. A subtle conspiracy of sun and wind, moving sand and rock a little bit every day over the aeons, rolls out an abstract masterpiece, breath-taking in scale and complexity. A cosmic doodle waiting to be appreciated, given meaning by my act of observation from 11 kilometres up.

Further south, unrelenting geology gradually gives way to biology…tentatively at first, but more robustly a short time later. Dry waterbeds become outlined on either edge by a thin, dark kohl of scrub. Then, the occasional palest blush of green appears on flat ground between these watercourses. Within a few miles, the scrub is ubiquitous, carpeting the land as far as I can see, thicker in the seasonal river beds, thinner on higher ground. That vegetation has taken hold in this most unforgiving of environments, the Sahel, is testament to the harshness of the millions of square miles of the Sahara proper, where I have seen not a single solitary plant.

Now starts the Great Cloud that covers the centre of Africa for much of the year, its clearly-defined northern walls stopping short of the Sahel, wary of that fearsome heat beyond. We dive into it as though flying into a monstrous grey cliff, and in a minute, visibility is cut to nothing. The cloud marks the advent of the gigantic forest that stretches almost completely across the middle of the continent, and with it, the anticipation of East Africa, and home…